A conventional turbocharger is disclosed in, for example, Japanese examined Utility-Model publication No. 8(1996)-7061. This turbocharger includes a turbine rotor, a turbine-housing, a plurality of nozzle vanes and a link mechanism. The turbine rotor is connected to a shaft and has a plurality of turbine wings. The turbine rotor is rotated by exhaust gas and disposed in the turbine housing. The turbine housing is provided with an involute inside wall which forms a scrolling portion for exhaust gas. The nozzle vanes are placed in the scrolling portion and supported by the turbine housing. The link mechanism controls the angle of the nozzle vanes so as to change the flowing direction of exhaust gas to the turbine rotor. Therefore, the rotation speed of the turbine rotor can be changed. The rotation speed of the turbine rotor is low when the angle of the nozzle vanes is large so that the flow of exhaust gas is directed toward the center of the shaft. The rotation speed of the turbine rotor is high when the angle of the nozzle vanes is small so that the flow of exhaust gas is toward the tangent line of the turbine rotor.
In the above-mentioned turbocharger, the link mechanism changes the angles of the nozzle vanes simultaneously. However, the temperature in the scrolling portion is more than 1,000.degree. Centigrade. Therefore, the link mechanism must be made of a heat-resistant material. Further, the exhaust gases include a considerable amount of carbon compound. The carbon compound influences the operation of the link mechanism. Therefore, the link mechanism needs to be highly reliable.